This invention concerns a process and apparatus for the treatment or hydrotreatment of a fluid charge and, more particularly, for the demetallation, desulfurization, hydrotreatment and conversion or hydroconversion of hydrocarbons.
The invention is particularly applicable to catalytic treatments of a liquid charge such, for example, as distillates issued from heavy crude oils, straight-run or vacuum residues of hydrocarbon distillation, these treatments being generally effected in the presence of hydrogen and/or gaseous mixtures of high hydrogen content, over a bed of solid catalyst, the catalyst being used as particles (catalyst extrudates, grains of various shapes, balls, etc.)
In such catalytic treatments, a quick deactivation of the catalyst is frequently observed as a result of the presence of catalyst poisons, of coke formation, of deposition of certain metals, etc.
This deactivation requires frequent replacements of a portion or of the whole catalyst bed.
In the process of the invention, the withdrawal of the catalyst from the reactor is generally effected periodically or sometimes continuously or at the end of the charge treatment.
The selected type of catalyst bed is that of a conventional ebullated or expanded bed, the expansion of the catalyst particles being obtained by the ascending flow of the gas and of at least one liquid which is generally the charge itself.
Beyond certain surface velocities of the gas and of the liquid, the catalyst bed, initially at rest, becomes expanded or dispersed and the catalyst, to which is imparted a permanent motion, circulates more or less quickly within the reactor. The present process is operated in such a manner as to obtain an expansion rate of about 10-30%, and for example 15%, by volume with respect to the bed at rest. A further description of the characteristics of the ebullated bed is needless, the latter being well-known in the art (see for example U.S. Pat. No. 2,987,465).
The process according to the invention and the apparatus according to the invention are also convenient for withdrawing catalyst particles from reactors used for cracking, hydrocracking, hydroreforming, aromatic hydrocarbons manufacture, isomerization of parraffinic, naphthenic or aromatic hydrocarbons, various reactions of hydrogenation, dehydrogenation, alkylation, transalkylation, hydrodecyclization, hydrodealkylation, hydrotreatment, hydrovisbreaking, etc., the liquid charge and the gas injected in these reactors progressing upwardly therethrough.
The fluid charge, which is a mixture of a liquid and a gas, is introduced into the reactor or into the enclosure containing catalyst particles, through distribution members located at the lower portion of the reactor or of the enclosure and circulates upwardly (upflow) before being discharged, after treatment of the charge, from the upper portion of the reactor (or of the enclosure which will be arbitrarily called "reactor" hereinafter).
The disadvantages resulting from the use of a downward circulation of the charge are known (in a technique of the moving bed type), the latter being discharged from the bottom of the reactor through a cylindrical grid located at the bottom of the reactor and which supports the catalyst bed. Such a process has the disadvantage of a risk of plugging the grid with catalyst grains pushed against said grid by the liquid material discharged from the bottom of the reactor. This may result in an uneven distribution of the fluids through the catalyst with liabilities of blocking certain zones of this bed during the catalyst discharge, as well as in an increase of the catalyst erosion due to the friction between the blocked grains and the free grains of the catalyst bed and between the free catalyst grains and the grid for discharging the liquid charge.